Biophysical simulation of wetland surface water flow to predict changing water availability in the Everglades

Abstract

A central challenge for water managers is to adaptively manage water availability to meet societal needs while simultaneously protecting ecosystems. Progress restoring Everglades wetlands requires simulations of how increased flow can rehydrate and restore functions of downstream wetlands without causing unintended harms. We developed a biophysical flow rate expression (BioFRE) that simulates flow of surface water based on hydraulic theory and measurements of spatially variable vegetation and microtopography. BioFRE simulations of surface flow compared well, without calibration, against independently measured hydrologic data at five locations representing various levels of wetland degradation. To help understand how changing vegetation and microtopography altered historical Everglades flows, we benchmarked BioFRE simulations against previous simulations of historical Everglades hydrology. Results indicated that the surface flow capacity of the Everglades has decreased by approximately half compared to the historical Everglades primarily because of the loss of sparsely vegetated deepwater sloughs. Remaining sloughs are fewer, less well connected, and more densely vegetated, causing increased hydraulic roughness, lower flow capacity, and diminished water storage, habitat value, and drought and flood resilience. We quantified the sensitivity of simulated flows to biophysical variables such as ridge proportion, microtopographic height, vegetation stem density, and slough connectivity, and we assessed their potential value as restoration performance measures. The BioFRE simulation approach can potentially be used in the Everglades and other wetland floodplains to anticipate changing conditions and to help improve management strategies that positively influence surface water storage and habitats while mitigating some negative outcomes of excessive droughts and floods.